added webpack bin, js bin playgrounds (#2478)

free-programming-playgrounds.md

@@ -47,9 +47,11 @@
 
 * [CodePen](http://codepen.io)
 * [CodeSandbox.io](https://codesandbox.io) (_React_)
+* [JSBin](http://jsbin.com)
 * [JSFiddle](http://jsfiddle.net)
 * [Plunker](http://plnkr.co)
 * [Sololearn](https://code.sololearn.com/#html)
+* [WebpackBin](https://www.webpackbin.com)
 
 
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